Scientific committees on Thursday recommended the Hong Kong government make the Omicron-specific coronavirus vaccine available to a wider population, hours after residents with three jabs began receiving the second-generation booster as their fourth dose.

Here is what you need to know about the second-generation Covid-19 vaccine now available in Hong Kong.

Hong Kong residents prepare to receive their Covid-19 vaccines.

1. What is a bivalent vaccine and which brand is available in Hong Kong?

Bivalent Covid-19 vaccines contain components of the original strain as well as Omicron, granting better protection against infections caused by the prevalent variant.

The only bivalent vaccine available in Hong Kong is produced in Germany by pharmaceutical company BioNTech and targets the subvariants BA.4 and BA.5. The two strains made up more than 70 per cent of cases sequenced by a government laboratory between November 22 and 28.

Authorities have ordered 1.9 million shots of the BioNTech bivalent vaccine so far, with the first batch of 770,000 arriving in the city on November 25.

US biotechnology company Moderna in June also said it was seeking regulatory approval from authorities in Hong Kong for an Omicron-specific booster jab.

2. Is the bivalent vaccine better than the original?

Government pandemic adviser Professor David Hui Shu-cheong on Friday told a radio programme that the bivalent vaccine, with its dual components, could trigger a higher level of antibodies that cover a broader range of Covid-19 variants, with other local health experts expressing a similar view.

But he added that the original vaccine, which also remains as an option, was still effective for restoring high levels of antibodies that would reduce the risk of severe illness.

3. Who is eligible for the bivalent vaccines?

As of Friday, bookings for the Omicron-specific vaccine were only accepted for uninfected adults as a fourth dose, or recovered individuals with two jabs as a third dose.

However, experts recommended at a meeting on Thursday that authorities broaden the eligibility criteria for receiving the jab. Health officials are expected to make their decision soon.

As part of their recommendations, the experts said healthy adults, residents at care homes for the elderly and immunocompromised adults with two, three or four prior jabs could take the bivalent vaccine as a booster shot. Those aged between 12 and 17 with three prior doses should also be able to get the Omicron-specific booster as a fourth dose, they said.

A man prepares to receive BioNTech’s bivalent vaccine.

4. Why haven’t authorities already made the bivalent jab more widely available?

While 3.99 million people received their third jab at least six months ago and were eligible to get the Omicron-specific vaccine, the government only ordered 1.9 million doses. Around 113,000 people got their four jabs at least half a year ago.

Hui, a member of the Scientific Committee on Vaccine Preventable Diseases, on Friday said authorities were still prioritising the bivalent jab for the tens of thousands of residents in Hong Kong’s care homes for the elderly.

Fellow committee member Dr Edmund Lam Wing-wo, emphasised in a radio interview on Friday that the bivalent vaccine was being offered as “another option” to meet the demand.

5. Who should get the second-generation vaccine?

Respiratory specialist Dr Leung Chi-chiu said the choice to have a fourth or fifth booster was essentially a personal one for most healthy adults, regardless of whether it was the original or Omicron-specific vaccine.

Leung said that, in theory, immunity against the virus derived from infection or a booster would wane over time. But he explained younger adults who lead active social lives had probably been exposed and had their defences bolstered as circulation of Covid-19 had been prevalent in the city for months.

“When compared to vaccination, the immunity replenishment effect of a natural viral exposure often comes faster,” Leung added.

He also advised that healthy adults who were frequently in contact with high-risk individuals, such as healthcare workers and carers for the elderly, should consider getting the bivalent jab.